Parts made only of either metal members or resin members are commonly used in the fields of automobiles, electronic devices, industrial machinery, and the like. That is, a commonly used method is to produce members made of metal or members made of resin, which are then assembled. By contrast, there has recently been more interest in composite members which include both metal members and resin members in the interests of fully exploiting the features of both metal and resin, producing more light-weight members, and reducing costs of manufacturing.
An example of a method for producing composite members of metal members and resin members is a technique utilizing insert molding. When a composite member is formed using insert molding, a metal member is first inserted in the mold. Molten resin is then injected into the mold, filling the mold with resin. The resin is cooled to solidification, and the composite member of the desired shape is taken out of the mold.
However, because resin and metal are inherently difficult to bond, the resulting composite members tend to separate where the component members are joined together. JP Patent No. 2,878,967 (Nakagawa, et al.) discloses a method to strengthen adhesion between resin and metal in metal-insert molding process comprising pretreating the metal surface with an alkoxysilane compound. JP laid open patent No. 2004-346255 discloses a polyimide composition containing a silane coupling agent and an epoxy-modified styrene elastomer to strengthen adhesion with metal.
There is a need to develop means for improving the bonding strength between the metal and resin without additional process steps.
Furthermore, when the resin has high thermal conductivity, early solidification of the resin is a problem. In other words, because of the high thermal conductivity of the resin, the resin tends to solidify while the mold is being filled with the resin, preventing the resin from spreading throughout the mold.
With respect to techniques for heating the resin supplied to a mold, U.S. Pat. No. 4,340,551 has disclosed a technique in which IH is employed to control the temperature of mold surface where the resin is supplied.